Question

If Phred throws a rock straight up, and Phran throws a rock straight up with twice the velocity of Pread's rock, how will the maximum height of Phred's rock compare to Phran's?

Answer 1

Answer:

The maximum height of Phran stone is four time that of Phred stone

Explanation:

From the question we are told that

   The initial velocity of Phred stone is  u

    The initial velocity of  Phran stone is  2u

Generally from kinematic equations

       $v^2 = u^2 + 2(-g)h$

Here the negative sign shows that the direction of the stone is against gravity

At the maximum height v which is the final velocity of the stone is zero  

So

      $0 = u^2 - 2gh$

So for Phred stone the height attained is  

=>   $h_1 = \frac{u^2}{2g}$

For  Phran stone the height attained is  

=>   $h_2 = \frac{(2u)^2}{2g}$

=>    $h_2 = \frac{4u^2}{2g}$

=>    $h_2 = 4 h_1$

Hence the maximum height of Phran stone is four time that of Phred stone